In the subsea fluid extraction industry, communication is required between a control centre and well heads located on the seabed. Traditionally, the control centre is located on a platform or vessel in relatively close proximity to the well complex. In some cases, the control centre is located on land, where the distance from the control centre to the well heads can be much greater and could be typically 200 km. High capacity communication systems, typically involving optical fibres, allow the possibility of much higher data rates between the subsea and surface facilities, which further enables methods of connecting subsea data sources (e.g. sensors), particularly those generating large quantities of data such as microseismic sensors and TV cameras.
A conventional approach is to use a standard subsea bus at the well head ends of a data transmission system to connect such various subsea data sources. This means that any other party providing equipment to the system has to interface with the bus and conform to its protocol, data rates and bus standards. Since different manufacturers have standard equipment with interfaces to a multiplicity of protocols and data rates, substantial costs are involved in adapting these interfaces to suit the standard bus. Furthermore, since this data is time multiplexed on the bus, the data rates are also somewhat limited such that some desirable, high bandwidth, data transmissions, such as digital video signals, cannot be economically transmitted.
FIG. 1 shows a conventional system for the communication of data between subsea well trees and a surface facility. Mounted on each of a number of subsea well trees (not shown) is a subsea electronics module (SEM) 1 including a SEM processor 2, which handles at a port 3 data from conventional tree sensors such as pressure and temperature and at a port 4 data for control of devices such as valves and fluid control chokes, there being a port 5 for a standard interface for data from other subsea data sources. The SEM processor 2 communicates bi-directionally with a surface facility computer system 6 (on shore or on a platform for example) via a modem 7 housed in the SEM 1, a communication link 8 and a modem 9 housed in a surface modem unit (SMU) 10 at the surface facility. The communication link 8 enables communication with the SEMs of other well trees and at some or all of the well trees there is system duplication to improve system availability—thus in FIG. 1 there are shown two SEMs (SEM A1 and SEM B1) for a particular well tree, SEM A2 and SEM B2 representing duplicate SEMs for another tree.
When the surface computer 6 is located at a considerable distance, such as, typically, 200 km from the well complex, a fibre optic link is used as link 8 to transmit data between the or each SEM at a well tree to the surface computer 6. Nevertheless, the data from other sources at port 5 needs to be adapted to the protocol, data rates and other standards used for the communication of control information and sensor information.